A light adjustable lens is an optical device whose refractive properties can be changed after its fabrication and insertion into a human eye. Such lenses are described, for example, in U.S. Pat. No. 6,450,642; U.S. Pat. No. 6,851,804; U.S. Pat. No. 7,074,840; and U.S. Pat. No. 7,281,795, the disclosure of all which is incorporated herein by reference. The light adjustable lens (LAL) has a refraction modulating composition dispersed in a polymer matrix. After the lens has been implanted into the eye and refractive stabilization has occurred, deviations from the planned refractive power, and preexisting optical aberrations or those induced by the clinical procedure (e.g. spherical power, astigmatism, spherical aberration), can be measured. In order to correct the optical, or dioptric power, as well as these optical aberrations, the LAL is irradiated, typically with a UV light. This irradiation alters the optical properties of the lens either through changes in its shape, its index of refraction, or both. Following one or several irradiations in which portions of the lens have been exposed to selectively and spatially modify the refractive power, the entire lens is irradiated to “lock in” the modified lens.
The use of UV irradiation has been discussed in the ultraviolet wavelength range of 320-400 nm for post-operatively adjusting the optical power of LALs. For example, a Helium Cadmium (HeCd) laser operating at 325 nm and a mercury (Hg) arc lamp spectrally filtered for the emission lines at 334 and 365 nm have been used for modifying the refractive power of LALs. Additionally, references also mention that tripled frequency laser diode pumped solid state YAG lasers operating at 355 nm, an argon ion laser operating in the 350-360 nm range, a deuterium discharge lamp, and broad-band xenon:mercury lamps operating with any narrow band spectral filter are all useful light sources for conducting UV irradiation on light adjustable materials and lenses.
However, there is still room for improvements related to these sources. When using a coherent source, such as a laser, there is the possibility that the source gets focused to a point on the retina, creating high irradiances that can cause damage. Extended spectrum, incoherent sources such as are lamps are attractive from the standpoint that they cannot be focused to a tight spot. It is noted though that these sources typically have high output irradiances so their output must be attenuated by as much as a factor of 1/1000 for use in irradiating the light adjustable lenses. Thus, improper use of such incoherent lamps, or a mechanical or electrical failure of the attenuation system could result in inadvertent application of high irradiances to the ocular structures, again resulting in unintended damage. These possibilities, however, can be prevented with a reassuringly strong margin of safety. Therefore, incoherent mercury arc lamps provide a valuable engineering solution for an ultraviolet light source to be used to irradiate LALs implanted into the human eye. Their utility is further underlined by their relatively low cost, and the fact that the filtered 365 nm line from the mercury arc lamp is effective for the photo-polymerization process.
Still, given the high value and demand for achieving optimal clinical outcomes in ophthalmology, as well as the importance of reducing ocular exposure, drive the search for newer generations of lens adjustment systems that can deliver more precise and more predicable clinical outcomes and reduce the ocular exposure even further.